A frequently employed method of heating a process fluid is by use of an indirect water bath heater. By "process fluid" means a liquid or gas employed in chemical, petroleum or other processing or manufacturing industries.
The expression "indirect water bath heater" means that the heater system employs a quantity of water or other heat transfer liquid that is heated, and heat from the liquid then heats the process fluid. Thus, the term "indirect" means that heat is not applied directly to the process fluid, or directly to a container in which the process fluid is contained, but is applied indirectly through a water or other liquid bath.
A water bath heater has advantages over a direct fired heater, a significant advantage being that an indirect heater provides more uniform temperature control with reduced likelihood that the process fluid will be either overheated or underheated at any instant of time. Further, the use of an indirect heater system reduces the likelihood of explosions or fires that can occur when a combustible process fluid, such as a oil or gas, is inadvertently overheated.
While these type of systems are referred to as "indirect water bath heaters", the expression "water" is used generically to mean any heat transfer liquid. Many indirect heater systems use glycol or a mixture of water and glycol as the heat transfer medium. The systems work essentially the same irrespective of the particular type of heat transfer liquid that is utilized.
The commonly known indirect water bath heater is typically in the form of a vessel, usually an elongated cylindrical horizontal vessel, although other vessels shapes are sometimes employed. A water bath heater vessel is usually referred to as a "shell". A burner tube, usually referred to as a "firetube" or "U-tube" is positioned in a lower portion of the shell and, when the shell is typically elongated and horizontal, the firetube is also elongated and horizontal. A most common method of employing a firetube in an indirect water bath heater is to utilize a long tube having an inlet at one end of the shell, the tube extending substantially the length of the shell and turning in a U-shaped fashion to an exit at the same end of the shell. Exterior of the shell a burner is affixed to the inlet end of the tube, the burner typically including a nozzle that injects gas mixed with forced or naturally inspirated air that produces a blast of hot gases that are moved into the firetube through the tube inlet. Hot gases travel the length of the firetube and reverse direction at the far end and return to the outlet. At the outlet, exterior of the shell, an exhaust stack is typically provided so that the products of combustion are exhausted to the atmosphere.
Located in an upper portion of the shell, above the firetube, is a process coil formed of loops of heat conductive pipe that extends back and forth horizontally through the full length of the shell. An inlet and an outlet of the process coil extends through a shell end wall. A process fluid, either liquid or gas, to be heated is passed into the process coil to flow back and forth through the coil loops within the upper portion of the shell. The process fluid is heated by heat transferred from the liquid heat transfer medium.
This type of indirect water bath heater has been used successfully for many years. The invention described herein provides an improved method, system and apparatus by which convective currents are established within the heat transfer medium of an indirect water bath heater to more efficiently transfer heat from a firetube to a process coil.